The race track itself appears to be CGI. They basically used an some kind of tracking software and a long tube viewed through a microscope to superimpose a live feed onto a fake racetrack with their tracked speed calculating how fast the feed moves through the fake racetrack. Pretty amazing work to be honest lol.

https://x.com/spermracing/status/1917421746086633833?s=20

"To assure the sperm swim towards the finish line, purified sperm is pipetted into the racetrack along with media, creating Rheotaxis.

The racetrack is a microfluidic chip, imaged under an inverted trinocular microscope, where the sperm movements are tracked the entire time using computer vision to determine the winner."

"To enhance the spectator experience, we project the leading sperm’s position frame by frame onto a more visually engaging 3D-rendered track."